Diffusion tower construction

ABSTRACT

An arrangement for expelling material from the top of a diffusion tower is disclosed. A stationary outer conduit and a coaxial rotatable inner conduit define together an annular diffusion chamber in which agitators are mounted for agitating a stream of material moving upwardly in the chamber in the direction towards the upper region of the same. In this upper region, the outer conduit is provided with outlets, and screw conveyors are provided communicating with these outlets and extending tangentially to the outer conduit so as to receive and expel the material which rises in the diffusion chamber. Expelling members extend in the upper region of the chamber transversely thereof and rotate with the inner conduit. The expelling members have edges which are leading and trailing in the direction of rotation, respectively, and the upper surfaces of these expelling members each have a major portion which is inclined from the leading towards the trailing edge, and an outer marginal portion adjacent the outer conduit which is planar and located in the plane of the leading edge closely beneath the screw conveyors. Guide baffles are also arranged in the upper region above the expelling members and have lower edges located above the same extending transversely of the chamber and contoured to correspond to the contour of the upper surface of the expelling members.

United States Patent Straube 14 1 Feb. 18, 1975 1 DIFFUSION TOWER CONSTRUCTION [75] Inventor: Elmar Straube, Bedburg, Germany 22 Filed: May 10, 1973 211 App]. No.: 359,027

[30] Foreign Application Priority Data May 18, 1972 Germany 2224209 [52] US. Cl 127/5, 23/270 R, 127/7, 198/204, 259/8 {51] Int. Cl ..Cl3d l/12 [58] Field of Search 127/2-7; 23/270 R [56] References Cited UNITED STATES PATENTS 2,043,409 6/1936 Heitmann 127/5 X 2,857,907 10/1958 Kaether r r 1 1 1 127/7 2,924,541 2/1960 Kaether 127/5 X 2,927,007 3/1960 Kaether 127/7 X 2,928,760 3/1960 Christoffersen r 127/5 X 2,950,998 8/1960 Stewart 127/7 3,142,589 7/1964 Schaffer 127/5 X 3,313,653 4/1967 .lung 127/5 X 3,726,715 4/1973 Mushack 127/5 3,794,521 2/1974 Dietzel 127/5 FOREIGN PATENTS OR APPLICATIONS 1,088,466 4/1957 Germany 127/5 1,078,960 12/1958 Germany l 1 1 127/5 209,830 6/1960 Germany 127/5 Primary Examiner-Morris O. Wolk Assistant ExaminerSidney Marantz Attorney, Agent, or FirmMichael S. Striker [5 7] ABSTRACT An arrangement for expelling material from the top of a diffusion tower is disclosed. A stationary outer conduit and a coaxial rotatable inner conduit define together an annular diffusion chamber in which agitators are mounted for agitating a stream of material moving upwardly in the chamber in the direction towards the upper region of the same. In this upper region, the outer conduit is provided with outlets, and screw conveyors are provided communicating with these outlets and extending tangentially to the outer conduit so as to receive and expel the material which rises in the diffusion chamber. Expelling members extend in the upper region of the chamber transversely thereof and rotate with the inner conduit. The expelling members have edges which are leading and trailing in the direction of rotation, respectively, and the upper surfaces of these expelling members each have a major portion which is inclined from the leading towards the trailing edge, and an outer marginal portion adjacent the outer conduit which is planar and located in the plane of the leading edge closely beneath the screw conveyors. Guide baffles are also arranged in the upper region above the expelling members and have lower edges located above the same extending transversely of the chamber and contoured to correspond to the contour of the upper surface of the expelling members.

16 Claims, 5 Drawing Figures 1 DIFFUSION TOWER CONSTRUCTION BACKGROUND OF THE INVENTION The present invention relates generally to a diffusion tower, and more particularly to a diffusion tower having a novel arrangement for expelling material from the upper region of the diffusion tower.

Diffusion towers and their principle of operation are well known. They are primarily used in the industry for extracting sugar from shredded sugar cane or from shredded sugar beets, but they are also known for use in extracting material from animal bones, for the bleaching and washing of cellulose fibers, and for other applications. The principle of operation is that a constant stream of the material to be extracted is admitted at the bottom of the diffusion tower in which it rises upwardly towards the upper end thereof. A liquid required for extraction, washing or the like, is admitted at the top of the tower and flows towards the bottom, in counter flow to the rising stream of material.

Evidently, when the material reaches the upper end of the diffusion tower, at which stage it has been extracted, it must be discharged or expelled from the tower. This has heretofore created a problem in the industry because it is desired that the expulsion be carried out in a simple manner without requiring a complicated device, and that the dimensions and especially the height of the opening through which the expulsion takes place, be as small as possible. The general construction of such towers is in form of an upright outer conduit, with an inner conduit being arranged coaxially within the outer conduit and rotatable relative thereto. The inner conduit carries agitating members which agitate the upwardly moving stream of material. One attempt in the prior art to overcome the above-identified problems has been to provide guide baffles located in the upper region of the tower, extending tangentially to the inner conduit and deflecting the upwardly moving material in outward direction, that is towards the outer conduit. Associated with these guide baffles are rotating expelling members which engage the thus-deflected material and expel it through outlets in the outer conduit. The problem with this approach is that the expelled material must be intercepted at several points, channeled to a collection point, and then removed by a suitable conveying device. All of this requires mechanical devices which, of course, increase the expense involved in the construction of such a tower, necessarly increase the outer dimensions of the tower which is frequently undesirable, and which involve substantial maintenance. Also, they either require an increase in the height of the tower or, if for some reason (for instance due to space limitations) this is not possible, they take up some of the space which was previously utilizable in the interior of the tower for extraction purposes.

Still another approach known in the prior art is to provide a screw conveyor in the upper region of the tower, which withdraws upwardly rising material from the latter. The screw conveyor operates within the tower in the expulsion region for the material and engages the latter in a more or less uncontrolled fashion. The construction does have the advantage that material is expelled from the tower at only one location, rather than a plurality of them, but quite a sizeable proportion of material is pushed away within the tower by the flights of the conveyor screw, and is thus pushed back into the chamber containing the mix of material and liquid, so that the removal of material is rather uncontrolled. Moreover, this construction has the tendency for the material which has thus been deflected by the flights of the screw to backup within the extraction of diffusion chamber laterally adjacent the screw, and to be subjected to a certain amount of pressure. All of this, of course, results in a very uneven extraction of substance from the material, and especially any pressure exerted upon the material by the aforementioned buildup tends to express liquid from them which, in turn, disadvantageously influences the concentration of extracted substance in the liquid in the upper region of the tower. This is particularly noticeable if the tower is of the type in which the level ofliquid is below the outlet opening.

SUMMARY OF THE INVENTION For all of these reasons, the present invention seeks to overcome the disadvantages of the prior art.

More particularly, it is an object of the present invention to provide an improved diffusion tower construction in which the disadvantages of the prior art, especially the two aforementioned proposals, are avoided but their advantages are maintained.

An additional object of the invention is to provide such an improved diffusion tower construction which utilizes simple, inexpensive and rather maintenancefree means for effecting the expulsion of the extracted material from the tower.

In keeping with these objects, and with others which will become apparent hereafter, one feature of the invention recites, in a diffusion tower, in a combination which comprises a stationary outer conduit and a coaxial rotatable inner conduit defining with the outer conduit an annular diffusion chamber having an upper region. Agitating means is provided for agitating a stream of material which moves upwardly in the chamber in direction towards the upper region. Outlet means is provided in the outer conduit in the upper region. Screw conveyor means is also provided in the upper re gion and extends through the outlet means from the interior to the exterior of the outer conduit, tangentially of the latter. Expelling means is mounted on the inner conduit for rotation therewith in the upper region, so as to expel material through the outlet means, and it comprises an expelling member extending transversely of the chamber and having a circumferentially leading and a circumferentially trailing edge, a radially outer marginal portion which extends from one to the other of these edges, and an upper surface having a major portion which is inclined from the leading toward the trailing edge except for the marginal portion where the surface slopes down to a planar surface portion which is located in the plane of the leading edge and closely beneath the screw conveyor means. Guide baffles are arranged in the upper region and have lower edges located above the expelling member; these guide baffles extend transversely of the chamber and their lower edges are contoured to correspond to the contour of the upper surface.

This construction overcomes the disadvantages of the prior art but retains its advantages.

In particular, when the inner conduit rotates with the agitating means, then a broad stream of material being extracted moves in upward direction, but outside the range of the expelling means. Thus, the particular arrangement of the various components in the upper re gion of the chamber assures a specific movement of the material even in this upper region, contrary to the prior art. The upwardly moving stream of material presents beneath the screw conveyor means a surface which constantly rises, so that the material will necessarily be engaged by the flights of the screw conveyor means and will be properly expelled by the same. In the region between the outlet means the upwardly moving material is engaged by the expelling means and, during its continuous upward movement, it is channeled by the guide baffles to the expelling means. In other words, some of the material is supplied directly to the outlet means, and some of it is supplied indirectly to the outlet means from the upper region of the chamber in which there is no outlet means provided, that is the region where the wall of the stationary outer conduit is not interrupted by outlet means. The sequence of movement of the material to the outlet means as a result of this differential path which the material traverses, is so phased that a uniform expulsion of material per unit of time takes place.

Moreover, the material will be raised only relatively slowly out of the zone of the chamber which contains liquid, so that any liquid adhering to the material can drip off the material before the latter is expelled. This means that the material can be expelled in relatively dry condition. and that there will be a smaller amount of loss of extracted substance which, of course, takes place if any of the liquid from the chamber is expelled together with the material.

At the juncture between the main portion of the surface and the depressed portion on the radially outer marginal portion of the expelling member, the surface is concavely rounded, and this configuration in conjunction with the inner surface of the stationary outer conduit forms a trough in which the upwardly moving material becomes collected, and from which it will be forceably urged towards the screw conveyor means for engagement thereby. Once the material has been engaged by the expelling member, it can no longer move back into the remainder of the contents of the chamher.

The surface is advantageously slightly conically inclined from the leading edge towards the trailing edge of the expelling member, so that in conjunction with the guide baffles a reliable supply of the material into the aforementioned trough is assured. Evidently, the longer the trough, the more material it can accommodate and supply to the screw conveyor means.

The screw conveyor means itself may comprise one or more conveyor screws, for instance two. If more than one are provided, then they may either be rotated in the same sense as, or opposite to, the rotation of the inner conduit. To assure that the material can be most advantageously engaged by the conveyor screws, and cannot recede from the same, it is advantageous according to a further concept of the invention if the conveyor screws are rotated in such a direction that each increment of the respective screw flight moves downwardly and outwardly against the inner surface of the outer conduit, before moving upwardly again. This means that the material is engaged by the conveyor screw, moved towards the inner surface of the outer conduit, or against the trough in which the conveyor screw rotates, and reliably engaged for expulsion. The number of revolutions per unit time at which the con veyor screws are rotated, may be made adjustable in accordance with well-known practice.

It is desired that the construction require as little space as possible. According to one feature of the pres ent invention, this is achieved in that the conveyor screws are so arranged that the axis of rotation of the respective screw, or the outer edge of the trough in which the screw rotates, or any line in between this edge and the axis of rotation, extends tangentially to the outer conduit. The best possible arrangement in terms of space utilization is obtained if the outer edge of the conveyor screw itself is tangential with the outer conduit.

It has become evident from the drawbacks of the prior art that under all circumstances and at all times a reliable supply of material to the conveyor screws must be assured. The present invention achieves this aim by means of a system of guide baffles and one or more guide rail portions provided on the upper surface of the expelling member itself. This system, which will be discussed subsequently, prevents a flowing-back of the material out of the upper region of the diffusion chamber, and assures that material will be constantly and reliably supplied to the conveyor screws, so that it can be expelled in a constant stream which can be regulated as required.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however. both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates an exemplary embodiment of the present invention, in a sectional view taken on line I-I of FIG. 4;

FIG. 2 is a section taken on line II-II of FIG. 4;

FIG. 3 is a section taken on line III-III of FIG. 1;

FIG. 4 is a section taken on line IV-IV of FIG. I; and

FIG. 5 is a section taken on line V-V of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before entering into a more detailed discussion of the drawing it is pointed out that only the upper portion of a diffusion tower provided with the present invention, has been illustrated in the several figures. The lower portion is not necessary for an understanding of the invention and does not present any deviation from conventional constructions well known in the prior art. It need merely be recalled that at the lower portion of the diffusion tower the material to be extracted, let it be assumed that it is shredded sugar cane or shredded sugar beets, is admitted and that the constant inflow of additional material causes the upward movement of a stream of such material into the upper region which has been illustrated in FIGS. 1-5. Also in conventional manner, an extracting liquid is admitted in this upper region (but no inlet for this purpose has been shown because this is conventional and does not form a part of the inventive concept), so that it can move through the upwardly advancing material in counter-flow thereto. to be withdrawn in the lower region of the tower.

With this in mind, and referring now to FIGS. l-5, it will be seen that the tower comprises a stationary upright outer conduit 1, and a rotatable inner conduit 2 which is received in the outer conduit 1 coaxially therewith. The two conduits define between themselves an annular diffusion chamber 4, of which only the upper region is shown, as only the upper regions of the conduits 1 and 2 are shown. Drive means 3 of convention well-known type is provided for rotating the inner conduit 2.

The inner conduit 2 carries a plurality of agitating members which extend transversely of the chamber 4 and rotate with the inner conduit 2. These agitating members are arranged in several superimposed planes, and in the illustrated embodiment, each plane is shown to be provided with two of these agitating members 60 (in one plane) and 6b (in the other plane). Evidently, the agitating members will be provided on more than the two planes which have been illustrated merely for the sake of explanation. in FIGS. 2 and 4, the uppermost agitating members are identified with reference numeral 6 and those located below them with reference numeral 6'. The purpose of the agitating members is, of course, to agitate the upwardly moving material in the chamber 4, in order to permit a more ready flow of the downwardly moving extracting liquid through them. It is not desired that the rotation of the agitating members 6 be transmitted to the mixture of material and liquid in the chamber 4, that is this mixture is not desired to rotate in the chamber 4. To prevent this, there are provided retarding members 7 which are secured to the inner surface of the outer conduit 1 and extend radially inwardly thereof across the chamber, being located intermediate the planes in which the agitating members themselves are located. The inner ends of the retarding members '7 are connected with annular retainers 8 which surround the rotatable inner conduit 2. The retarding members 7 are inclined to the horizontal (in circumferential direction of the tower) by approximately 45, in such a manner that the upwardly moving sugar cane or sugar beet substance can slide upwardly along them without having to overcome any substantial resistance. The uppermost retarding members, which are located immediately beneath the expelling members ll, 110, are identified with reference numeral l0 and have a specific purpose which will be discussed subsequently.

The upper end of the tower, or rather of the chamber 4, is closed by a cover 5, as illustrated in FIG. 3. The outer conduit 1 is provided with two narrow circumferentially elongated outlet openings 9a and 9b, but it should be understood that it is immaterial in terms of the present invention whether only a single outlet or more than two are provided.

It has already been pointed out earlier that it is desirable to maintain the overall dimensions of the tower as small as possible. in particular, it is desired that the material which is supplied via the uppermost retarding members 10 into the zone where it is expelled, is supplied uniformly to the two outlet openings 9:: and 9b which are provided in the illustrated embodiment, without having to significantly increase the overall dimensions of the tower. This supply is assured by the novel expelling members which have been illustrated and will be described subsequently.

In particular it is pointed out that two expelling members have been illustrated, one being identified with reference numeral 11 and the other with reference numeral 110. These two expelling members are of different construction, as will be seen in the drawing and will be presently discussed; it is pointed out that each diffe rent construction can be used individually, that is one or all expelling members can be of one type of construction, but it is also possible to resort to a construction such as is shown in the illustrated embodiment where expelling members of the two different types of constructions are used together.

In FIG. 3, the expelling member 11 is located at the left-hand side of the drawing, and the expelling member Ila at the right-hand side of the drawing. The same relationship, with the members 11 and 11a being located at opposite sides of the inner conduit 2, will be found in FIG. 1. The members 11, Ila are secured either directly to the inner conduit 2, or as illustrated they are secured thereto by means of a flange 31 (see FIG. 5) which can be welded or otherwise connected with the inner conduit 2. The member II has an edge 15 which is the leading edge as seen with reference to the direction of rotation of the inner conduit 2, and an edge 16 which is the trailing edge as seen with reference to the same direction. The analogous edges of the expelling member are designated with reference numerals 15a and 16a, respectively. A surface portion 14 or rises upwardly and rearwardly from the respective leading edge 15, 15a and merges into a further surface portion 13 or 130. The outer circumferential marginal portion of the respective member 11, 11a is configurated as an expeller strip 17 or 17a which extends from the respective leading edge 15, 15a in circumferential direction to the respective trailing edge 16 or 16a. The plane of the upper surface of the respective strip 17, 17a is horizontal and located in the plane of the respective leading edge 15, 150. If desired, the lower edge of the respective members 11, 11a can be made slightly rearwardly and upwardly inclined, although this is not illustrated.

The surface portion 13 of the member 11 is of slightly conical configuration and merges in radially outward direction into a strongly curved portion 18 whose curvature corresponds to the circumference of the conveyor screws 4 and 5, respectively. This curvature of the portion 18, in conjunction with the portion 17 and the inner wall of the outer conduit 1 defines a trough 29 (see FIG. 3) in which the material to be expelled can accumulate. Evidently, the longer the outer edge 12 of the member 11 is in circumferential direction. the longer of course will be the trough 29 and the more ma terial can accumulate therein. On the other hand, the more pronouncedly conical surface 13a of member 110 merges via a slightly rounded surface portion 18a into the marginal portion (compare FIGS. 1 and 3), thus forming with the latter and with the inner surface of the conduit 1 a trough 29a which is shallower than the trough 29 (see FIG. 3). As pointed out before, either the type of expelling member designated with reference numeral 11, the type designated with reference numeral 11a, or both types together can be employed, depending upon the particular requirements, for instance the particular material to be expelled.

The leading edges 15 and 15a of the members 11 and 110, respectively, extend approximately tangential to the inner conduit 2, whereas the trailing edges 16 and 16a extend approximately radial with reference to the inner conduit 2, as is perhaps most clearly shown as seen in FIG. 1.

It has already been mentioned that two conveyor screws are provided, designated with reference numerals 19a and 1%, respectively, and each associated with one of the outlet openings 90 and 9b. These screws are so installed that their outer edges, or the outer edges 28 of the respective troughs 20a, 20b in which the screws rotate, extend tangential to the outer conduit 1. It is an important concept of the invention that the screws are so far radially outwardly located that their axes of rotation 21a, 211) are tangential to the outer conduit 1. The journals for the screws, and the drive means therefore, have been omitted because they are well-known per se to those skilled in the art. It should be noted that the troughs 20, 20a are located only exteriorly of the conduit l, and that no portion of the troughs is located interiorly thereof. Those portions of the screws 19a, 19b which are located within the outer conduit 1 are freely exposed therein.

A comparison between FIGS. 1 and 3 shows particularly clearly that the system of guide baffles according to the present invention is located above the expelling members 11, 11a. The guide baffles are designed with reference numerals 22a, 22b, 23a, 23b, 24a, 24b and in addition there are provided guide rail portions 27. The latter are mounted on the upper surfaces of the members II, 110 and rotate with the same. These rail portions 27 are shallow in their height and may be either straight or curved in configuration, being so shaped that in the region where they intersect the guide baffles in space (not physically) they extend approximately normal to the latter.

The guide baffles are made fast with the outer conduit 1 or the cover 5. In particular, the guide baffles 22a and 22b are fixedly connected (for instance by welding) with the outer conduit 1 at the locations 30 and 30a, respectively. They are convexly curved in the direction of rotation of the inner conduit 2 and the locations 30 and 3011 are so chosen that an imaginary straight line extending longitudinally of the respective screws 19a and l9b and passing through the locations 30, 30a will extend in parallelism with the axis of rotation of the screws. The inner ends of the baffles 22a, 22b are connected almost tangentially with a ring member 32 which surrounds the rotatable inner conduit 2 loosely and which, in turn, is fixed to the cover 5 as shown in FIG. 3.

This arrangement of the guide baffles separates the expulsion zone of the chamber 4 into two parts, so that the material rising in the chamber 4 will enter either into one part and from there into the outlet opening 90, or in the other part and from there into the outlet opening 9b. This is an inherent result of the arrangement and requires no additional means to achieve this partic ular movement. It also, of course, prevents a flowingback of the material into the other portions of the chamber so that once the material has entered these respective separated halves of the upper portion of the chamber, it will be reliably guided towards and engaged by the screws 19a, 19b, respectively. Additional guide baffles 24a and 24b are provided, which are also convexly curved and which are connected with and extend outwardly from the ring member 32. They extend to the region of the conveyor screws 19a, 19b and assure that the material will always be supplied to the screws adjacent the front ends thereof. that is the inner ends located inside the conduit 1. There is still a third type of guide baffle provided, designated with reference numerals 23a and 23b (see FIG. I) which assures that the upwardly moving material will be guided in direction outwardly towards the inner side of the conduit 1, and will be immediately engaged in and accumulated by the troughs 29, 29a.

It will be seen from FIG. I that between the edge l5 and the edge 16a, and again between the edge 15a and the edge 16 there is a respective free zone of the chamher 4, that is a zone which is not covered by the members II, Ila. In these two zones, the upwardly moving material enters into the upper region of the chamber 4. As this takes place, the respective leading edge. for instance the leading edge l5, engages the upwardly moving material which during the continued movement of the member I] having the edge 15 slides over the surface portion 14 onto the surface portion 13. As the material reaches the surface portion 13 and during continued rotation of the member 11, the baffle 23b pushes the material into the trough 29. The material rising from beneath the plane of FIG. I underneath the baffle 23b is also engaged by the member I1 and is pushed towards the screw 19b by the baffle 24b. Material which rises in FIG. 1 to the left of the baffle 24b, is also engaged by the member 11 and is pushed towards the screw 19b by the baffle 22b during continued rotation of member 11.

When the members 11 and 11a are located in the left-hand half and the right-hand half of the chamber 4, respectively, (FIG. 3) then the free space in which the material can rise will be located downwardly of the screw 19a (in the view shown in FIG. I) and upwardly of the screw 19b. This means that material rising upwardly will be directly engaged by the respective screws, because it will come in direct contact with them, and will be expelled by them. Because material continuously rises to replace any material that has been expelled, a regulatable reliable engagement of the material by the screws 19a, l9b is assured. The effect is aided by the fact that the inner surface of the conduit 1 provides guidance for the upwardly moving material.

It will be seen in FIG. 1 that the opening 9b is slightly larger than the opening 90, and that the trough 20b is connected with the conduit 1 by means of a sheet material portion 26. Any material which rises upwardly in this region will enter directly into the trough 20b and will be immediately and directly engaged by the screw 19b to be expelled thereby.

The direction in which material is expelled by the screws 19a and 19b is identified in FIG. I by the character 8, whereas the direction of rotation of the agitating members (and thus of the conduit 2) is identified with reference character A. With respect to this direction of rotation of the conduit 2, the screw will be seen to rotate in the same direction, whereas the screw 19b rotates in the opposite direction. If it is desired that the screws 19a and 1% both rotate in the same sense as the conduit 2, then the screw 19b can be extended to the opposite side in FIG. I, that is in the direction shown in broken lines, so that it will now expell material in the direction of the arrow C. In this case, the right-hand end of the trough 20b will, of course, be closed because material can no longer be expelled in the direction of the arrow B. This modification has an advantage in that the screws and the conduit 2 rotate in the same sense, but it also has the disadvantage that material is expelled in two mutually opposite directions and must therefore be separately collected and separately removed by suitable conveyors, whereas the arrangement illustrated in FIG. 1 has the advantage that material is expelled in one and the same direction and requires only a single conveyor for its removal.

if the material which is to be expelled is ofa fibrous nature, then it is advantageous if the outer circumference of the flights of the screws 19a, 19b is serrated so as to be better able to engage this material, which due to its fibrous character, tends to interfelt, and to expell it. This can, of course, be done also if the material is not of fibrous character or if the fiber content is low.

In the illustrated embodiment, l have chosen to show two expelling members 11, 11a whose outer circumferential edges 12 have a length corresponding to approximately 90 of the circumference of the outer conduit 1, in the case of each of these members 1], 11a. This means that approximately one-half of the cross sectional area of the chamber 4 will be covered at all times by the members 11, 11a. Of course, it is possible to use for instance three of the members ll, or Ila, or a combination of them, in which case the length of their edges 12 must only amount to approximately 60 each, so that again only about one-half of the cross section area of the chamber 4 will be covered by the three members together. It will be appreciated that this is necessary in order to permit the free zones in which the material can rise, as discussed earlier.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the type described above.

While the invention has been illustrated and described as embodied in a diffusion tower construction, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letter Patent is set forth in the appended claims:

1. in a diffusion tower, a combination comprising a stationary outer conduit and a coaxial rotatable inner conduit defining with said outer conduit an annular diffusion chamber having an upper region; agitating means for agitating a stream of material which moves upwardly in said chamber in a direction towards said upper region; outlet means in said outer conduit in said upper region; screw conveyor means in said upper region and extending through said outlet means from the interior to the exterior of said outer conduit, tangentially of the latter; expelling means mounted on said inner conduit for rotation therewith in said upper region, so as to expel material towards said outlet means, said expelling means comprising an expelling member extending transversely of said chamber and having a circumferentially leading and a circumferentially trailing edge, a radially outer marginal portion which extends from one to the other of said edges, and an upper surface having a major portion which is inclined from said leading toward said trailing edge except for said marginal portion where said surface slopes down to a planar surface portion which is located in the plane of said leading edge and closely beneath said screw conveyor means; and guide baffles arranged in said upper region and having lower edges which are located above said expelling member, extending transversely of said chamber and being contoured to correspond to the contour of said upper surface.

2. A combination as defined in claim I, wherein said upper surface includes a transition portion connecting said major portion and said planar portion and being concavely curved in correspondence with an outer circumference of said screw conveyor means.

3. A combination as defined in claim I, wherein said major portion of said upper surface has a substantially conical inclination in direction from said leading to ward said trailing edge.

4. A combination as defined in claim 1, wherein said marginal portion has a circumferentially extending edge whose length corresponds to substantially of the circumference of said outer conduit.

5. A combination as defined in claim 1, wherein said outlet means comprises two circumferentially spaced outlets, and said screw conveyor means comprises two conveyor screws each of which is associated with one of said outlets.

6. A combination as defined in claim 5, wherein said conveyor screws rotate in mutually opposite directions.

7. A combination as defined in claim 6, wherein each of said conveyor screws includes a conveyor trough in which it rotates and which has an opening communicating with the associated outlet; and wherein one of said outlets is larger than the other and provided with a bridging portion bridging a free space between adja cent edges of said one outlet and the associated opening.

8. A combination as defined in claim I, wherein the direction of rotation of said screw conveyor means is towards the interior of said conduits.

9. A combination as defined in claim 1, further com prising an annular retainer surrounding said inlet conduit in said upper region; and wherein said guide baffles extend substantially tangentially from said annular retainer and each comprise a portion which is convexly curved in the direction of rotation of said inner conduit and is connected with said outer conduit at a location positioned on an imaginary straight line paralleling an axis of rotation of said screw conveyor means and passing through said location.

10. A combination as defined in claim 9, further comprising curved additional baffles located between pairs of circumferentially adjacent ones of said guide baffles, said additional baffles projecting from said annular retainer by a distance which is substantially half of the length of said guide baffles intermediate said annular retainer and said location.

11. A combination as defined in claim 10, wherein at least one of said additional baffles extends to the proximity of said screw conveyor means.

12. A combination as defined in claim 10, wherein at least one of said additional baffles extends to the proximity of said planar portion of said upper surface.

13. A combination as defined in claim 10, wherein said additional baffles have lower edges located adja- 15. A combination as defined in claim 14, wherein said guide rail portion is convexly curved in the direction of rotation of said inner conduit.

16. A combination as defined in claim I, said screw conveyor means comprising conveyor screw means having a plurality of screw flights, and wherein said screw flights have outer peripheries which are serrated. i i i i 

1. IN A DIFFUSION TOWER, A COMBINATION COMPRISING A STATIONARY OUTER CONDUIT AND A COAXIAL ROTATABLE INNER CONDUIT DEFINING WITH SAID OUTER CONDUIT AN ANNULAR DIFFUSION CHAMBER HAVING AN UPPER REGION; AGITATING MEANS FOR AGITATING A STREAM OF MATERIAL WHICH MOVES UPWARDLY IN SAID CHAMBER IN A DIRECTION TOWARDS SAID UPPER REGION; OUTLET MEANS IN SAID OUTER CONDUIT IN SAID UPPER REGION; SCREW CONVEYOR MEANS IN SAID UPPER REGION AND EXTENDING THROUGH SAID OUTLET MEANS FROM THE INTERIOR TO THE EXTERIOR OF SAID OUTER CONDUIT, TANGENTIALLY OF THE LATTER; EXPELLING MEANS MOUNTED ON SAID INNER CONDUIT FOR ROTATION THEREWITH IN SAID UPPER REGION, SO AS TO EXPEL MATERIAL TOWARDS SAID OUTLET MEANS, SAID EXPELLING MEANS COMPRISING AN EXPELLING MEMBER, EXTENDING TRANSVERSELY OF SAID CHAMBER AND HAVING A CIRCUMFERENTIALLY LEADING AND A CIRCUMFERENTIALLY TRAILING EDGE, A RADIALLY OUTER MARGINAL PORTION WHICH EXTENDS FROM ONE TO THE OTHER OF SAID EDGES, AND AN UPPER SURFACE HAVING A MAJOR PORTION WICH IS INCLINED FROM SAID LEADING TOWARD SAID TRAILING EDGE EXCEPT FOR SAID MARGINAL PORTION WHERE SAID SURFACE SLOPES DOWN TO A PLANAR SURFACE PORTION WHICH IS LOCATED IN THE PLANE OF SAID LEADING EDGE AND CLOSELY BENEATH SAID SCREW CONVEYOR MEANS; AND GUIDE BAFFLES ARRANGED IN SAID UPPER REGION AND HAVING LOWER EDGES WHICH ARE LOCATED ABOVE SAID EXPELLING MEMBER, EXTENDING TRANSVERSELY OF SAID CHAMBER AND BEING CONTOURED TO CORRESPOND TO THE CONTOUR OF SAID UPPER SURFACE.
 2. A combination as defined in claim 1, wherein said upper surface includes a transition portion connecting said major portion and said planar portion and being concavely curved in correspondence with an outer circumference of said screw conveyor means.
 3. A combination as defined in claim 1, wherein said major portion of said upper surface has a substantially conical inclination in direction from said leading toward said trailing edge.
 4. A combination as defined in claim 1, wherein said marginal portion has a circumferentially extending edge whose length corresponds to substantially 90* of the circumference of said outer conduit.
 5. A combination as defined in claim 1, wherein said outlet means comprises two circumferentially spaced outlets, and said screw conveyor means comprises two conveyor screws each of which is associated with one of said outlets.
 6. A combination as defined in claim 5, wherein said conveyor screws rotate in mutually opposite directions.
 7. A combination as defined in claim 6, wherein each of said conveyor screws includes a conveyor trough in which it rotates and which has an opening communicating with the associated outlet; and wherein one of said outlets is larger than the other and provided with a bridging portion bridgiNg a free space between adjacent edges of said one outlet and the associated opening.
 8. A combination as defined in claim 1, wherein the direction of rotation of said screw conveyor means is towards the interior of said conduits.
 9. A combination as defined in claim 1, further comprising an annular retainer surrounding said inlet conduit in said upper region; and wherein said guide baffles extend substantially tangentially from said annular retainer and each comprise a portion which is convexly curved in the direction of rotation of said inner conduit and is connected with said outer conduit at a location positioned on an imaginary straight line paralleling an axis of rotation of said screw conveyor means and passing through said location.
 10. A combination as defined in claim 9, further comprising curved additional baffles located between pairs of circumferentially adjacent ones of said guide baffles, said additional baffles projecting from said annular retainer by a distance which is substantially half of the length of said guide baffles intermediate said annular retainer and said location.
 11. A combination as defined in claim 10, wherein at least one of said additional baffles extends to the proximity of said screw conveyor means.
 12. A combination as defined in claim 10, wherein at least one of said additional baffles extends to the proximity of said planar portion of said upper surface.
 13. A combination as defined in claim 10, wherein said additional baffles have lower edges located adjacent said upper surface and being contoured to correspond to the contour of the same.
 14. A combination as defined in claim 10, and further comprising at least one guide rail portion mounted on said upper surface and oriented so as to intersect said baffles in space, said rail portion extending in the region of said intersection at least substantially normal to the respective baffle.
 15. A combination as defined in claim 14, wherein said guide rail portion is convexly curved in the direction of rotation of said inner conduit.
 16. A combination as defined in claim 1, said screw conveyor means comprising conveyor screw means having a plurality of screw flights, and wherein said screw flights have outer peripheries which are serrated. 